Among the conventionally known security devices, there is a microwave sensor which emits microwaves to a detection area. If an intruder is present in the detection area, this microwave sensor catches a microwave reflected by the intruder and thereby detects the presence of the intruder.
There has been also known a “security system” that detects an intruder by employing a laser distance meter whose light source is a laser beam, instead of microwaves (see, for example, Patent Literature 1).
This “security system” is equipped with a sensor unit, a swivel camera unit, and a control unit. The sensor unit sets a monitoring area according to a scan angle for effecting two-dimensional scanning by a beam from the light distance meter. When an intruder is detected in the monitoring area, the sensor unit outputs distance data and angle data with regard to the intruder. The swivel camera unit is mounted on an electric swivel base, and swivels in conjunction with the sensor unit. When the sensor unit detects more than one continuous change in the distance data or the angle data, the control unit checks the presence or absence of an intruder, calculates a position of the intruder based on the changed distance data and the changed angle data sent from the sensor unit, causes the swivel camera unit on the electric swivel base to swivel in accordance with the positional data, and causes a monitor to display image data of the intruder.
Although slightly different from the security device and the security system, there has also been suggested an “object identification process by an area sensor” which can correctly identify a pedestrian or the like with use of a laser beam (see, for example, Patent Literature 2).
According to this “object identification process by an area sensor”, a detection range covers a walking area for guiding pedestrians and a perimeter area around the walking area. An area sensor projects a pulse laser beam by a laser sensor to scan the detection range, and measures a reflection time of the beam. For each scanning point, the area sensor obtains a difference between a reflection time in the presence of an object and a reflection time in the absence of an object, and thereby calculates the shape and size of the object, and a vector related to the change in the object position for each scanning cycle. Based on the arithmetic signal, the area sensor distinguishes between an object moving along the walking area and an object moving across the walking area.
Further, the inventors of the present application have already proposed a laser area sensor which can accurately detect an intruder or the like and which can minimize false detection, irrespective of an installation site, weather conditions, or other factors, by maximally excluding negative effects on the laser beam in outdoor installation in bad weather or the like (see Patent Literature 3).
This laser area sensor is characterized in having a first laser distance meter, a scanning mechanism unit, an information acquisition unit, a first information correction unit, a human body judgment unit, and a human body detection signal output unit. The first laser distance meter emits a pulse laser beam, measures the time from the emission until a beam is reflected by at least one object in the direction of the beam, and thereby obtains distance information to the object and received light level information of the reflected light. The scanning mechanism unit changes the measurement direction by the first laser distance meter. By allowing the scanning mechanism unit to change the measurement direction and allowing the first laser distance meter to make a periodic measurement, the information acquisition unit defines a detection area and sequentially acquires distance information and received light level information for each measurement direction. In the first information correction unit, the distance information and the received light level information acquired by the information acquisition unit at a measurement cycle are compared, in each measurement direction, with the distance information and the received light level information acquired before and after this measurement cycle. If the comparison reveals a discontinuous change that exceeds a predetermined degree, the first information correction unit cancels the distance information that corresponds to the discontinuous change in this measurement cycle in the relevant measurement direction, and corrects a portion of received light level information that does not correspond to the discontinuous change. The human body judgment unit extracts a portion of distance information that has been corrected by the first information correction unit and that is assumed to be a human body. Based on the sequential movement status of the extracted portion of information, the human body judgment unit judges whether the extracted portion of information corresponds to a human body. If the human body judgment unit confirms the presence of a human body, the human body detection signal output unit outputs a human body detection signal.